Axial-flux-machine with an ironless fractional slot winding

In this paper, a novel 42 slot, 20 pole ironless winding for use in an axial-flux machine is presented. The proposed design improves the utilization of the available air gap area and is based on the implementation of the winding as a printed circuit board (PCB). Besides, it is compared with a conventional 21 slot, 20 pole ironless axial-flux winding regarding the criteria: torque generation and induced voltage at constant speed. The comparison is based on analytical calculated results, which were obtained by using the winding function theory and an exponential function approach for the magnetic flux density produced by the permanent magnets. The analytical description of the MMF is derived from the geometry whereas the torque and the induced EMF are calculated by using complex Fourier series. Furthermore, a special case of Parseval´s theorem is used to get the torque and voltage from the Fourier coefficients in a very simple way. The analytical calculated results are compared to those obtained by FEM.